The Chinese herbal remedy, Tripterygium wilfordii Hook F has been used to treat a variety of autoimmune and inflammatory diseases in China for hundreds of years. However, the nature of the active components of this plant and their mechanism of action have been completely delineated. We were able to show that Tripterygium wilfordii Hook F contains a series of complex diterpenoids that account for its anti-inflammatory and immunosuppressive effects. Moreover, the mechanism of action of these diterpenoids relates to their capacity to suppress transcription of genes regulated by the transcription factors AP-1, NF-AT, and NFkappaB. Preliminary phase 1 trials have demonstrated that ethanol/ethyl acetate extracts of Tripterygium wilfordii Hook F are safe and suggest they exert dramatic clinical benefit in patients with rheumatoid arthritis. The objectives of the current work are to develop the means to carry out phase II/III trials with reproducible extracts of Tripterygium wilfordii Hook F in patients with systemic lupus erythematosus, rheumatoid arthritis, and psoriasis. Toward this end, a large supply of the roots of Tripterygium wilfordii Hook F have been obtained from China. The diterpenoid content of the roots has been verified by HPLC methodology developed specifically for this purpose. A reproducible method for preparing the extract has been developed and the composition and safety of the extract verified. The material appears to be appropriate for clinical trials. In summary, extracts of Tripterygium wilfordii Hook F have unique potential as anti-inflammatory/immunosuppressive agents. Their potential can now be tested in appropriately controlled, randomized, double blind trials.